Production of anodised surfaces of aluminum or aluminum alloys



United States Patent 3,532,607 PRODUCTION OF ANODISED SURFACES OFALUMINUM OR ALUMINUM ALLOYS Kenneth Edward Roberts, Dorchester, Dorset,England, assignor to Anomate Products Corporation, Summit,

NJ. No Drawing. Filed Feb. 20, 1967, Ser. No. 617,056 Claims priority,application Great Britain, Feb. 26, 1966,

8,575/ 66 Int. Cl. C23b 9/02; B44c l/04 US. Cl. 204-18 4 Claims ABSTRACTOF THE DISCLOSURE a two-coloured or multi-coloured design on such ananodised plate using a photosensitive resist is described.

This invention relates to the anodising of surfaces of aluminum oraluminium alloys containing at least 99% of aluminum and moreparticularly to the anodising of such a surface prior to the productionthereon of a twocolour or multi-colour design using a photosensitiveresist and an appropriate dye or dyes. One of the two or more coloursmay be the natural colour of the anodised surface.

The production of such designs on anodised aluminum surfaces is ofparticular interest for the production of nameplates, for example, forattachment to machines, but it is of interest also in the other andwider fields, for example, the use of decorated aluminum panels in theconstruction of dwelling houses or other buildings. Hitherto, however,in order to avoid impairment of the anodised coating, it has beennecessary either to seal the oxide coating by suitable treatment afteranodising, either immediately after washing or after the oxide coatinghas been dyed, or to protect the oxide coating during the production ofthe design by a layer of a protective material such as gelatine. Theintroduction of the sealing step at this stage in a manufacture of thedecorated surfaces is inconvenient, particularly where an entirelyautomatic process is required, and may, moreover, limit the methodswhich can be used for producing the design, or may produce an inferiorproduct owing to partial destruction of the anodised layer during theprocess of producing the design. The use of a gelatine coating obviouslycomplicates the production of the design by the introduction of thecoating step.

It is an object of the present invention to provide a process forproducing an anodised surface, of aluminum or an aluminum alloycontaining at least 99% by weight of aluminum for use where a coloureddesign is subsequently to be produced on the anodised surface, by theuse of which these disadvantages may be overcome or at least minimised.

According to the invention, there is provided a process for producing ananodised surface of aluminum or an aluminum alloy containing at least99% by weight of aluminum, for use where a two-colour or multi-colourdesign is subsequently to be produced on the anodised surface using aphotosensitive resist and one or more dyes, comprising the step ofanodising the surface in an anodising solution consisting of diluteaqueous sulphuric acid containing 5-20% by volume of sulphuric acid,using a direct current at- 10.5 to 24 volts, the current beingmaintained within the range 9-20 amps per square foot, the temperaturein the range 40-90 F. and the treatment time in the range -60 minutes.

3,532,607 Patented Oct. 6, 1970 It has been found that by suitableselection of the anodising conditions within the ranges specified abovein accordance with the particular material being treated, the anodisedsurface can be used in the unsealed state for subsequent processing toproduce the design without any danger of impairment of the anodisedoxide layer, and without the necessity for adopting special andcomplicated techniques in the production of the design.

The particular values of each of the parameters involved will dependupon the nature of the material being treated, the parameters beingmutually adjusted in accordance with the physical form and chemicalcomposition of the metal.

Thus, for example, in the treatment of standard 99.5% aluminum sheet ingauges 10 SWG. to 30 SWG., manufactured by the British Aluminium CompanyLtd., using a bath containing 20% by volume of sulphuric acid, a currentdensity of 9.8 amps per sq. ft., at 12 volts, a bath temperature of 74F. and a treatment time of 30 min utes have been found to besatisfactory.

For the same material, using a bath consisting of 5% by volume aqueoussulphuric acid, a temperature of 40 F., a current density of 20 amps persquare foot at 24 volts and a treatment time of 60 minutes have alsogiven satisfactory results.

Again, for sheets of from 10 SWG. to 22 SWG. manufactured by BirmetalsLtd. and sold under the name B.B.2, a current density of 9.4 amps persquare foot at 10.5 volts consisting of 20% by volume aqueous sulphuricacid, a temperature of 72 F. and a treatment time of 30 minutes givesatisfactory results; for sheets of from 24 SWG. to 30 SWG. sold by thesame company under the name B.B.17, a current density of 9.4 amps persquare foot at 10.5 volts, a bath of 20% by volume aqueous sulphuricacid, a temperature of 74 F. and a treatment time of 30 minutes aresatisfactory; and for sheets sold under the name 550 manufactured byImpalco Ltd., a current density of 9.6 amps per square foot at volts, abath temperature of 74 F. and a treatment time of 30 minutes givesatisfactory results.

For aluminum foil of thickness 0.003 inch and using a 20% by volumesulphuric acid bath, a current density of 9.4 amps per square foot at10.5 volts, a bath temperature of 88 F. and a treatment time of 20minutes are satisfactory; whilst for aluminum foil thicknesses between0.005 and 0.008 inch using the same bath, a current density of 10.5 ampsper sq. ft. at 12 volts, a bath temperature of 90 F. and a treatmenttime of 20 minutes are satisfactory.

After the anodising treatment has been completed, the metal sheets arerinsed in cold running water and may be gently sponged over under coldrunning water, or are rinsed clear under reasonably powerful, cold waterspray jets. 1

Depending on the particular method of producing the design on theanodised surface chosen, the anodised surfaces after cleansing may, ifdesired, be dyed by immersion in a hot or cold solution of the dye forthe period indicated by the manufacturer of the dye. This period isusually between 7 and 30 minutes.

The sheets, either dyed, or of natural anodised aluminum are now driedby draining and airing in circulating slightly warmed air at atemperature not exceeding 80- F.

Various procedures may be adopted for the production of the final designon the anodised surface. In a preferred method of producing the design,the anodised surface of the sheet is dyed as described above beforedrying. The surface on which the design is to be formed is now coatedwith a suitable photosensitive resist resin, for example, Kodak P.C. orKodak P.R. Photosensitive Resist, either by dipping or by spraying orwhirling the resist on to the surface. If a design is to be produced onboth sides of the metal sheet, it will preferably be coated with theresist by dipping and allowing surplus resist to drain off. The resistlayer is then allowed to dry.

The coated surface is now exposed to ultra-violet light through a lineor half-tone positive or negative stencil and developed using adeveloper appropriate to the particular resist employed. Afterdevelopment the surface is rinsed clean with cold water.

The colour is now removed from the uncovered areas of the anodised layerby immersing the sheet in a solution of 50 gms. per litre of potassiumpermanganate 50 100 gms. per litre of nitric acid and 50-100 gms. perlitre of sodium bisulphite in water. The unwanted colour disappearsafter soaking and agitating for about 1 minute.

The remaining photosensitive resist which has been exposed and fixed onthe sheet to protect the original dye is now removed by treatment with asuitable organic solvent, for example, xylene or trichlorethylene, andthe sheet fully sealed by immersion in a heavy metal salt solution, suchas nickel acetate solution, with or without boric acid crystals; or bysealing in hot water or steam. The result is a surface having atwo-colour design (one colour being the natural colour of anodisedaluminum and the other that of the original dye), in which the anodisedoxide layer is intact and undamaged over the whole extent of thesurface.

If the design is required to be in two colours other than one colour andnatural anodised aluminum, the sheet can be immersed in a suitabledyefor the necessary time prior to removal of the remainder of theresist. If more than two colours, or two or more colours and naturalanodised aluminum, are required, then the sheet may be recovered withresist and exposed through a second stencil, the procedure then being asbefore, further exposures being used as necessary.

Other methods of producing the desired design may, of course, be usedwith plates anodised in accordance with the invention; for example, theknown method in which the plate is covered with a layer of protectivematerial, for example, gelatine or carboxymethylcellulose, beforedeposition of the resist. This latter method is not, however, essential,since the anodised oxide coating obtained by the process of the presentinvention is sufliciently robust to be usable without scaling in thesimpler method described above.

Whilst in the preceding description, reference has been made of the sakeof clarity to the treatment of metal sheets, it will be appreciated thatthe anodising process of the present invention and the subsequentproduction of a design on the anodised surfaces can be applied toaluminum and aluminum alloys in forms other than sheets, for example, tofoils, blocks, panels having an appreciable thickness, and to othershaped articles, made, for example, from metal sheet or foil.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is:

1. A process for producing a two-colour or multicolour design on asurface of a to 30 SWG. 99.5% aluminum sheet which comprises the stepsof:

(a) anodising said surface in a bath of by volume aqueous sulphuric acidat a temperature of 74 F. for 30 minutes with a current density of 9.8amps per sq. ft. at 12 volts;

(b) washing the anodised surface with cold water;

(c) dyeing the anodised surface;

(d) drying the dyed anodised surface with warm air at 80120 F.;

(e) coating the dyed anodised surface with a photosensitive resistresin;

(f) exposing the coated surface to ultraviolet light through anappropriate positive or negative stencil;

(g) developing the exposed coating to remove areas of said coating whichhave not been exposed;

(h) rinsing said surface;

(i) decolorizing areas of said surface not covered by residual coatingby treatment with a decolorizing solution;

(j) dyeing the decolorized areas in different colour to that of theoriginal dyed surface prior to decolorizetion;

(k) removing residual coating; and

(l) sealing said surface.

2. A process as claimed in claim 1 wherein for the production of amulti-colour design, steps (e) to (k) are repeated at least once priorto step (I), a different stencil being used at each repetition in step(f); and decolorized areas produced by step (i) being at each repetitiondyed a different colour.

3. A process for producing a two-colour or multi-colour design on asurface of aluminum foil of thickness between 0.005 and 0.008 inch whichcomprises the steps:

(a) anodising said surface in a bath of 20% by volume aqueous sulphuricacid at a temperature of F. for 20 minutes with a current density of10.5 amps per sq. ft. at 12 volts;

(b) washing the anodised surface with cold Water;

(c) dyeing the anodised surface;

(d) drying the dyed anodised surface with warm air at 80 to F.;

(e) coating the dyed anodised surface with a photosensitive resistresin;

(f) exposing the coated surface to ultraviolet light through anappropriate positive or negative stencil;

(g) developing the exposed coating to remove areas of said coating whichhave not been exposed;

(h) rinsing said surface;

(i) decolorizing areas of said surface not covered by residual coatingby treatment with a decolorizing solution;

(j) dyeing the decolorized areas in different colour to that of theoriginal dyed surface prior to decolorization;

(k) removing residual coating; and

(l) sealing said surface.

4. A process as claimed in claim 3 wherein for the production of amulti-colour design, steps (e) to (k) are repeated at least once priorto step (1), a different stencil being used at each repetition in step(f); and decolorized areas produced by step (i) being at each repetitiondyed a different colour.

References Cited UNITED STATES PATENTS 2,550,388 4/1951 Simon et al.204--58 2,812,295 11/ 1957 Patrick 204-58 FOREIGN PATENTS 474,608 10/1937 Great Britain. 476,161 11/1937 Great Britain.

OTHER REFERENCES Production of Multi-Coloured Effects on AnodizedAluminum, V. F. Henley, The Metal industry, June 18, 1943, pp. 386-388.

HOWARD S. WILLIAMS, Primary Examiner T. 'IUFARIELLO, Assistant ExaminerU.S. Cl. X.R. 204-5 8

